The fatty acid composition of vegetable oils determines their physical and chemical properties and hence their applications. The wide range of applications of vegetable oils, 90% edible and 10% non-edible, reflects their fatty acid compositional diversity. Vegetable oils are a renewable resource that can serve as feedstock to produce environmental friendly industrial products such as lubricants, paints, detergents and body care. Demand for these oils in the non-food sector is likely to increase in response to the shrinking reserves of mineral oils.
Hundreds of different fatty acids have been identified and characterised in the plant kingdom, but most of them are not available for economic uses. Genetic engineering provides the means to tap these vast resources by producing fatty acids of economic importance in the storage lipids of oil crops. Achievements through breeding alone or in combination with mutagenesis, such as in the development of rapeseed oil with low content of erucic acid (22:1) and sunflower oil with high level of oleic acid, indicate that plants can tolerate a wide variation in fatty acid composition of storage lipids.
Palm oil is generally extracted from the mesocarp of the oil palm fruits. Palm oil which contains about 50% saturated, 40% monounsaturated, 10% polyunsaturated fatty acids is a semi-solid fat at room temperature. Its fatty acid composition consists of 44% palmitic acid (16:0), 5% stearic acid (18:0), 39% oleic acid (18:1) and 10% linoleic acid (18:2). Palm oil products are primarily used in the food sector, typically as solid fat for margarine, shortening and cooking oil production. Non-edible or technical applications are, however, substantial and increasing. These include, for example, soap, oleochemical-production and use as an energy source for cars.
Production of novel high-value products by genetic engineering provides the opportunity to diversify the use and to increase the economic value of palm oil. Production of specialty oils for industrial applications would be a very attractive proposition for the oil palm, since it is the most productive of oil crops. Recombinant DNA technology has been used successfully to manipulate fatty acid biosynthetic pathways in a variety of transgenic oil crops, such as rapeseed, to produce a modified oil composition. Reported success in raising the levels of lauric acid and stearic acid in rapeseed oil proved that both fatty acid chain length and the level of fatty acid unsaturation can be modified.
Genetic engineering efforts rely heavily on the availability of a reliable transformation technique for achieving stable integration and a regulatory sequence for controlling expression of introduced genes. With oil palms, there has been significant progress in the development of a reliable transformation system using biolistics techniques. In addition, analysis of several plant promoters located 5′ of genes using transgenic plant systems showed that regions in the range of several hundred basepairs to about one kilobase could produce faithful expression patterns of reporter genes in vivo. The availability of seed-specific promoters that drive gene expression over the entire period of oil deposition in oil-bearing crops like rapeseed and soybean have been a major contribution to the success in altering oil composition by genetic engineering. These promoters have ensured that most of the effects on lipid metabolism are confined to storage lipids without significantly affecting lipid metabolism in leaves or other tissues which can otherwise leads to deleterious agronomic effects on the transgenic plants.
Similarly for the oil palm, efforts to modify mesocarp oil composition by genetic engineering would benefit greatly from the availability of temporally-regulated and tissue-targeted gene promoters. Such promoters are preferably able to drive specific expression of introduced genes in the mesocarp during the period of oil synthesis (15-20 weeks after anthesis). In addition, promoters for selective expression of desired genes in other tissues of the oil palm would also be desirable.